Photonic flat band dynamics

Abstract

During the last decades, researchers of different scientific areas have investigated several systems and materials to suggest new ways of transporting and localizing light. These problems are probably main goals in any search for new configurations and new emerging properties, independently of the degree of complexity of suggested methods. Fortunately, fabrication techniques in photonics have consolidated during the last decades, allowing the experimental implementation of different theoretical ideas which were neither tested nor validated. Specifically, we will focus on recent advances in the implementation of Flat Band (FB) photonic systems. FB periodical structures have at least two bands in their linear spectrum, with one of them completely flat. This implies the emergence of linear photonic states which are completely localized in space and that can be located in different regions across the lattice. This localization occurs as a result of destructive interference, what naturally depends on the particular lattice geometry. In addition, flat band systems also posses dispersive states which make possible the observation of ballistic transport as well. Therefore, FB photonic lattices constitute an unique platform for studying localization and transport, without requiring the inclusion of any sophisticated interaction/effect, rather a smart and simple geometry.

Symmetry-protected higher-order exceptional points in staggered flatband rhombic lattices

“…Note that t L (t R ) is real and represents conserved (Hermitian) coupling. Experimentally, such non-Hermitian lattices can be obtained using the optical induced method or the femtosecond laser-writing technique [20][21][22][23][24]. The coupling strengths depend on the distance of the waveguides, thus a staggered arrangement of the distance between the waveguides generates staggered couplings.…”

“…A flatband is disper-sionless throughout the Brillouin zone (BZ) and it provides a unique setting for exploring anomalous magnetic phases and strongly correlated states of matter [16][17][18][19]. In flatband systems, diffraction is suppressed due to local destructive interference of the Bloch wave functions, resulting in typically compact localized eigenstates (CLSs) in real space [20][21][22][23][24]. Flatbands with completely real eigenvalues can appear in PT -symmetric lattices.…”

Topological Flatband Loop States in Fractal‐Like Photonic Lattices

“…Flat bands are energy bands characterized by the vanishing dispersion and immobile charge carriers, hosting an ideal stage to explore strongly-correlated phenomena. [1,2] The study of flatband model has a venerable history in condensed matter physics, [3,4] DOI: 10.1002/lpor.202200315 but has recently attracted a great deal of interest, particularly in photonics, [5][6][7][8][9][10][11][12][13][14][15][16][17][18][19] exciton-polaritons, [20][21][22] sythentic electronic structures, [23,24] and Bose-Einstein condenses. [25,26] Indeed, in such flatband systems, a variety of fundamental phenomena have been demonstrated, ranging from Landau-Zener Bloch oscillations, superfluidity, superconductivity in twisted bilayer graphene, to quantum distance and anomalous Landau levels.…”

Robust Slow Light Enhancement Based on Flat Band States in the Continuum

“…However, the conventional wisdom has been defied by the surprising discovery of the flat band (FB) [20], a dispersion-free energy band characterized by a group velocity of zero for the wave packet throughout the Brillouin region. These novel properties of flat band physics have attracted a great deal of theoretical and experimental interest in a variety of fields, including ultracold atoms [5,[21][22][23][24][25], various metamaterials [26][27][28][29], exciton-polariton condensates [22,[30][31][32], photonic waveguide arrays [4,11,[33][34][35][36], and more. People have realized the flat band by constructing some special lattice structures with "geometrical frustration" [37], strengthening the magnetic field [38,39], constructing strain structures [40][41][42][43], introducing twist angles [44][45][46][47], etc.…”